1. Field of the Invention
The invention relates to a device that generates an intense radio frequency (RF) pulse. The primary source of energy is a chemical explosion, provided by a magneto-cumulative generator (MCG). The apparatus transforms the electrical pulse of the MCG into a powerful RF pulse.
2. Background Information
Attempts to create a device for generating high voltage pulses of short duration have resulted in several patents. One of the first patents on this topic was issued on Jun. 5, 1951 to R. L. Alty as U.S. Pat. No. 2,555,305, which teaches the use of a transmitter as a load, driven by a pulse generating circuit consisting of an inductor, a capacitor and a switch. Several other patents have issued since Alty's, with modifications on his basic idea. One such patent is U.S. Pat. No. 3,579,111 issued to Lexington et al on May 18, 1971. This more recent patent uses a tank circuit and a charging inductor to achieve resonance. The load is connected in series with the tank circuit. U.S. Pat. No. 4,491,842 issued on Jan. 1, 1985 to Gripshover et al shows yet another approach to generating high peak power, broadband radio frequency pulses. In this case, the generator is constructed with looped pairs of coaxial cables connected by spark gap switches. U.S. Pat. No. 4,482,816 issued on Nov. 13, 1984 to Richardson et al uses several pulse forming networks connected in parallel with a common double-sided printed circuit board to create a pulse circuit.
A more recent method of providing a power supply uses a magneto-cumulative generator (MCG) (A. D. Sakharov, Soviet Physics Uspekhi, vol. 9 No. 2, 1966, p. 294). The Magneto-Cumulative Generator (MCG) acts as a converter and transforms the chemical/mechanical energy of the explosion into an electrical energy impulse. MCG's have inherently low impedance and an energy density that is four to six orders of magnitude higher than traditional high voltage capacitors, while MCG's are also smaller in size than an equivalent electrically-driven system.
Several studies have been performed on the use of MCG's as power supplies in high-power RF devices. An important milestone in this field occurred with the 1993 disclosure of studies carried out in the Soviet Union by A. P. Prishchepenko and his colleagues (Prishchepenko A. B., Shchelkachev M. V., “Dissipation and Diffusion Losses in a Spiral Explosive Magnetic Generator”, Electichesvo, No. 8, 1993, pp31–36). Another example is U.S. Pat. No. 4,862,021 issued on Aug. 29, 1989 to LaRocca wherein a system is taught that uses an MCG as a power supply. U.S. Pat. No. 5,650,681 issued on Jul. 22, 1997 to DeLerno has a similar purpose, but uses magnets and coils to generate an electrical current instead of an MCG.
FIG. 1, based on the work of Thomas Holt (Holt, Thomas A.; Explosively-Driven Helical Magneto-Cumulative Generators; Texas Tech University; June 2002.), shows a drawing of a helical MCG. The armature 10 contains a highly explosive chemical 12 that is ignited with the detonator 14 at the left side. The aluminum end piece 16 and the aluminum end plug 18 hold the armature 10 in place. The crowbar ring 22 prevents flux leakage before the explosion is complete. The sleeve 24 separates the aluminum end piece 16 and the armature 10 to ensure connectivity between a load 20 and a wire helix 26 located coaxial to the armature 10, supported by its own sleeve 28.
Before detonation, the wire helix is energized by an auxiliary pulsed power supply and the detonator 14 is ignited once the current in the helix 26 reaches its peak value. The explosion causes the armature 10 to expand radially, starting at the left nearest the detonator 14 and working axially towards the right. The expansion pushes the armature 10 out to touch the wire helix 26, shorting out the individual windings. The voltage applied to the helix must be high enough to enable spark discharges to form between the turns of the helix and enable a thermalization process to occur during which the spark discharges behave as a solid conductor and short circuit the turns of the helix. According to the principle of flux conservation, the initial and final magnetic flux in a system must be the same. When the volume between the helix 26 and the armature 10 is reduced by the expansion of the armature 10, the magnetic flux is compressed, causing an increase in current and, thus, inducing a voltage. The entire explosion happens quickly: the flux is compressed, the current is delivered to the load and the MCG breaks up into shrapnel. When the rate of expansion of the armature exceeds 1 km/s, a voltage pulse of up to 100 kV occurs.
A typical RF transmission system consists of a transmitter and an antenna. The transmitter may be viewed as a closed oscillatory circuit and the antenna is an open oscillatory circuit. Usually the transmitter and antenna must be connected via a transmission line, which becomes an extension of the closed oscillatory circuit. For maximum energy transfer, the output impedance of the transmitter must match the input impedance of the transmission line. Accordingly, the antenna and transmission line must also be matched—the impedance seen looking from the antenna terminals toward the transmission line must equal the conjugate of the antenna's impedance (the resistive components must be equal and the reactive components must be equal in amplitude, but opposite in sign). The radiation emitted from the oscillatory circuit always converges toward the lower frequencies because the resistive losses are smaller at those frequencies.
An impulse generator can also be used as a transmitter. The charge in the impulse generator can be viewed as a simple capacitor, transmission line and switch or as a capacitor, inductor and switch. An example of an impulse generator, a Marx generator, operates on the principle that a short, high voltage pulse can be created by charging a stack of parallel capacitors to a low voltage and then switching them in series. Other electrical pulsed power supplies that can be used include a Blumlein generator, an LC bank, an inductive storage/plasma opening switch or a Tesla transformer/storage transmission line. An electrical pulsed power supply can facilitate high operation of the RF radiating device (up to 1000 pulses/sec). Ten percent of the energy stored in the generator is converted into RF emissions for compact systems. For larger, electrically driven systems, the emitted RF radiations can exceed 1 GW with the efficiency of conversion exceeding 10%.
The use of delay lines or transmission lines for generating high voltage pulses is known from U.S. Pat. No. 5,138,270 issued to Nakata on Aug. 11, 1992. The prior art described in the patent connects a pulse forming network to a transmission line via a switching device. The transmission line is then connected to a load. The patent itself uses capacitors and inductors to represent characteristics of the circuit and replaces the pulse forming network with a Blumlein charge circuit. A preferred embodiment uses two parallel coaxial cables for the Blumlein charge circuit.
The modulation of energy from an oscillatory circuit is achieved with suitable antennas. If the antennas are absent, the RF energy available in the oscillatory circuit is wasted. The antenna can have any form, however not all forms are optimal for all frequencies. Optimization of the antenna will result in a higher efficiency and a better device.
A parasitic radiating circuit occurs when a radiating element that is not connected to the antenna affects the radiation pattern or impedance of the antenna. To reduce or eliminate the current in the parasitic radiating circuit, a quarter-wave trap can be provided. U.S. Pat. No. 4,542,358 issued on Sep. 17, 1985 to Boby uses a quarter-wave trap to protect a coaxial cable from high-powered, low frequency parasitic pulses. The quarter-wave trap consists of two microstrips arranged in parallel, separated by a dielectric substrate. The microstrips have a length that is a multiple of a quarter of the operational wavelength. It is important to reduce or eliminate parasitic currents in devices generating high voltage radio frequency pulses of short duration.
Provision of a device to generate high voltage radio frequency pulses is required. In the present invention, an MCG forms a transmitter to generate very high voltage RF pulses to disable computers, rather than merely forming the power supply for the transmitter. The conversion efficiency of chemical energy into electromagnetic energy reaches as high as 10% and the efficiency of RF generation from the electromagnetic energy pulse can reach 10%. A medium size helical MCG containing 0.5 to 2 kg of high energy explosive is able to supply power to generate an RF pulse of 10–40 kJ. If a smaller radiating device is required, the voltage impulse can be provided by an explosive piezo-generator containing 10–60 g of explosive. Classical explosive matter has a specific combustion energy on the order of 107 Joules per kilogram of explosive. The magnetic energy density stored in the inductive accumulator or in the helix of an MCG can reach 4*105 J per litre of volume. It has been observed that an RF pulse of such size is capable of causing damage to computers and digital electronic systems.
Thus, an MCG is a power source that can only be used once. In light of this fact, an equivalent circuit or model is required to perform multiple tests of the ability of an MCG to act as an RF device. Non-destructive testing of such a combination is required to determine operability. Explosively driven RF devices operate on the same principle as electrically driven RF devices, except a chemical explosion is used as the primary source of energy. The MCG behaves as a converter to transform the chemical/mechanical energy of the explosion into a magnetic energy impulse. A combination of opening and closing switches cause the transfer of magnetic energy into an electrical energy impulse that energizes an oscillatory circuit. MCG's are advantageous because they have inherently low impedance and are smaller than electrically driven systems.